DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 245 
(0.b.), exactly as in young Marsupials; the annulus thickens in front, just where it 
lies under the front crus of the os bullee. 
There are here five vomerine bones, as in the embryo Hedgehog, and Armadillo; the 
main bone or vomer proper (fig. 5, v.) is strong and carinate, and bluntly pointed at 
both ends ; it is short for so long a skull, and its keel is very thick. The two antero- 
lateral vomers (v’.) are the largest I have seen, as yet, reminding one of their large 
cupped counterparts in the Ophidia and Lacertilia ; they are ovato-oblong, and sculp- 
tured in their infero-external face, and are like two chaff scales of the Oat. The fore 
part of the main vomer (v.) is hidden by these two bones ; the recurrent or J ACOBSON’S 
cartilages (7'c.c.) are seen outside them. 
The narrow hind part of the main vomer (v.) is partly hidden by the two large 
postero-lateral vomers (v”.), which, as far as I know, are in this case relatively larger 
than in any other Eutherian ; they are perfectly Metatherian in size and relations, 
nearly meeting in the middle, having there a ribbed edge, and sending outwards a 
large rounded lobe from their middle part; they are each nearly as long as the 
main vomer, and are twice as long as the antero-lateral pair (v’.). The hind part of 
each postero-lateral vomer (v.) just overlaps the base of the orbitosphenoid (0.s.) and 
reaches the presphenoid (p.s.). The above are the whole of the investing bones I 
have been able to find in this type. 
Endocranium of Rhynchocyon cernei. 
y y 
The deep parts of this skull are as remarkable as the superficial ; the diagnostic 
characters of several Orders meeting in one endocranium. That tract of the nasal 
labyrinth which is in front of the proper olfactory region is very long (Plate 36, 
fies. 4-7), and is segmented in all but its foremost and hindmost part ; there are 
thirty double rings, and this is as true a “ proboscis” as that of the Elephant. So 
long is this proboscis that the completely closed part is half as long as the whole 
labyrinth, which, altogether, is twice as long as the basis cranii, proper. 
The nostrils (e.n.) are nearer the lower than the upper face of the snout, and are 
very near its end ; the valvular coil of the nostril is very complete, and terminates m 
a free outer process. There the double tube is very narrow, but widens gently to 
twice its first width, it is then constricted twice, and swells again before the definite 
enlargement for the middle turbinals begin. There is then a deep constriction, and 
then the whole structure swells out to almost tenfold the width of the neck of the 
double snout-tube. Those swollen bags of cartilage do not meet each other below 
(fig. 5); above (fig. 4), they are deeply excavated, behind a short, perfect roof-region 
to form the two large circular multiperforate olfactory fossze, each floored by the cup- 
shaped cribriform plate (cr7.p.). Above, the septum (p.e.) terminates in a bulbous, 
free “ crista galli” (cr.g.), but the sloping hind margin of the wall continuous with the 
cribriform plate, and notched where the multitudinous branches of the olfactory nerve 
pass through from the cranial into the nasal cavity (see fig. 7, p.e.), becomes much 
